A liquid chromatography mass spectrometer (LC/MS) comprises a liquid chromatography unit (an LC unit) that separates a liquid sample into components and elutes them, an ion chamber (an interface unit) that ionizes the sample components eluted from the LC unit, and a mass spectrometer unit (an MS unit) that detects the ions introduced from the ion chamber. There are various ionization methods used in the ionization chamber, including the Atmospheric Chemical Ionization (APCI) method, and the Electro Spray Ionization (ESI) method.
In an actual example of the APCI method, the tip of a nozzle connected to an end of column of the LC unit is oriented into the ionization chamber, and the front end of the tip of the nozzle has a needle electrode. For ionization, the needle electrode generates corona discharge to generate carrier gas ions (buffer ions) which chemically react with mist of a heated sample droplet in the nozzle. In the ESI method, the tip of a nozzle connected to an end of column of the LC unit is oriented into the ionization chamber, and there is approximately 5 kV of high voltage applied at the tip of the nozzle to generate a strong non-uniform electric field. The electric field separates electric charges of a liquid sample, and the Coulomb force makes the liquid sample mist. As a result, the solvent of the liquid sample evaporates by contacting with surrounding air, generating an ion gas.
Because the APCI and ESI methods ionize liquid samples at near-atmospheric pressure, in order to hold a certain pressure difference between the ion chamber at a high pressure (i.e., near atmospheric pressure) and the MS unit at very low pressure (i.e., in a high vacuum state), there is an intermediate chamber configured between the ionization chamber and the MS unit for gradual increase of the degree of vacuum (for example, refer to Patent Article 1).
FIG. 8 depicts a schematic diagram of an example of liquid chromatography mass spectrometer using the ESI method, and FIG. 9 is a perspective view of the liquid chromatography mass spectrometer shown in FIG. 8.
The liquid chromatography mass spectrometer comprises an ionization chamber 200, a mass spectrometer unit 50, a control chamber 16, and a housing unit 170.
There is a triangular shaped aluminum chamber 210 in the ionization chamber 200, and the chamber 210 has an top surface 210a, a first side surface, a second side surface, a third side surface, and a bottom surface. There is a circular aperture at the center of the first side surface, and the first side surface is air-tightly attached to the front surface of a first intermediate chamber 12 through a rubber O-ring around the aperture (not shown in the figures). There is a spray (part of ionization chamber) 15 attached on the top surface 210a of the chamber 210.
The control chamber 160 is located beneath the ionization chamber 200, having a rectangular control box of size 22 cm×48 cm×24 cm, and there is a rectangular aperture 161a of size 6 cm×10 cm formed on the top surface of the control box 161. There are a power supply 66 and a nebulized gas supply 65 configured in the control box 161. And, a cable connected to the power supply 66 connects to a heater and a temperature sensor through the aperture 161a. A tube 64 connected with the nebulized gas supply 65 connects to the spray 15 through the aperture 161a. 
A liquid sample decomposed in the LC unit is supplied to the spray 15 through the tube 155. The nebulized gas source 65 supplies a nebulized gas (nitrogen gas) to the spray 15 through a tube (a connection pipe) 64 of diameter 0.3 cm. As a result, the liquid sample and the nebulized gas are guided into the spray 15 and spayed therefrom.
At the same time, although not shown in the figures, a high voltage power supply applies high voltage of 5 kV to a cable that is connected with the tip of the spray nozzle. For heating, the power supply 66 provides voltages to the heater (part of ionization chamber) and the temperature sensor (part of ionization chamber) through, e.g., a cable (a connecting tube) 67 of diameter 0.5 cm.
The spray 15 shown in FIG. 8 is used for the ESI method, which is generally detachable from/to the chamber 210, and if an APCI spray is preferably used, the ESI spay 15 may be detached and then the one for the APCI that has an integrated discharging needle electrode may be attached to the chamber 210.
In the mass spectrometer unit 50, there are a first intermediate chamber (a vacuum introduction unit) 12 adjacent to the ionization chamber 200, a second intermediate chamber 13 adjacent to the first intermediate chamber 12, and mass spectrometer chamber (the MS unit) 14 adjacent to the second intermediate chamber, each of which is separated by a partition but successively configured.
The first intermediate chamber 12 has rectangular aluminum housing 90 of size 15 cm×11 cm×60 cm, and there is a first ion lens 21 in the housing 90, whereas there is an exhaust 31 on the bottom surface of the housing 90 for evaluation using an oil rotary pomp (RP).
There is a heater block 20 that has a built-in temperature adjustment mechanism (not shown) on the front surface of the housing 90, and a circular solvent removing tube 19 (of the outer diameter 1.6 mm and the inner diameter 0.5 mm) is configured in the heart block 20. The solvent removing tube 19 connects the interiors of the chamber 210 and the housing 90. The solvent removing tube 19 has a capability of accelerating solvent removal and ionization due to heating and collisions when ions and minute liquid sample droplets, sprayed from the spray 15, upon passing through the solvent removal tube.
On the partition between the first intermediate chamber 12 and the second intermediate chamber 13, there is a skimmer 22 formed having an orifice though which the interiors of the housing 90 and the second intermediate chamber 13 are connected.
Inside the second chamber 13, there is an octupole 23 and a focus lens 24, and on the bottom surface of the second intermediate chamber 13, there is an exhaust 32 for vacuum evacuation using a turbo molecular pomp (TMP). On the partition between the second intermediate chamber 13 and the mass spectrometer chamber 14, there is an inlet lens 25 formed having an orifice through which the interiors of the second intermediate chamber and the mass spectrometer chamber 14 are connected.
In the mass spectrometer chamber 14, there are a first quadruple 16, a second quadruple 17, and a detector 18, and on the bottom surface of the mass spectrometer chamber 14, there is an exhaust 33 for vacuum evacuation using a turbo molecular pomp (TMP).
In such as liquid chromatography mass spectrometer, ions generated by the ionization chamber 200 are sent to the mass spectrometer chamber 14, successively through the solvent removing tube 19, the first ion lens 21 in the housing 90 of the first intermediate chamber 12, the skimmer 22, the octupole 23 and the focus lens 24 in the second intermediate chamber 13, and the inlet lens 25 in this order, wherein the quadruples 16 and 17 expel ions not required for detecting specific ions with the detector 18.
Because the aforementioned liquid chromatography mass spectrometer requires maintenance of the first ion lens 21 and other members, the ionization chamber 200 is configured as a single unit so that the ionization chamber 200 may switch between a maintenance position and an analysis position. For example, the ionization chamber 200 uses a hinge (not shown) to rotate around a vertical axis between the first side surface and the front surface of the first intermediate chamber 12 by approximately 90°. With this configuration, an observer may place the ionization chamber 200 in the maintenance position for performing maintenance on the first ion lens 21 and other members, and, in turn, place the ionization chamber 200 in the analysis position for performing analysis.
In order to improve the appearance by concealing the interior of the control box 161, or as a countermeasure against water-splashing test of the Low Voltage Directive, the housing unit 170 is configured. The housing case 170 has a rectangle case 171 of size 16 cm×20 cm×27 cm, and a cover 172 that is rotatable relative to the case 171. The tube 64, the cable 67, and the aperture 161a are configured in the case 171. With such configuration, for conducting analysis, after removing the spray 15, the ionization chamber 200 is inserted while the cable 67 and the tube 64 are inserted into the case 171.